The present invention relates to a solder supplying method at a joint portion used for soldering electronic components to a printed-wiring substrate or assembling electronic components, an apparatus therefor and a soldering method.
Heretofore, a ball setting method or a solder printing method has been used for supplying solder to external electrodes of an LSI package in order to form bumps (Fen Maeda, "Cream Solder Printing Techniques and Applications for Forming BGA Bumps", Surface Mounting Techniques, Vol. 5, No. 5, 1995, pp.1-6).
On the other hand, a method described in the Examined Japanese Patent Application Publication No. Hei. 7-85487 has been proposed as a bump forming method using solder paste.
FIGS. 22A to 22E are views showing a conventional solder supplying method, for example, as described in the Examined Japanese Patent Application Publication No. Hei. 7-85487. In the drawing, the reference numeral 1 designates a transfer member; 2, holes provided in the transfer member 1; 3, solder paste to be charged into the holes 2 provided in the transfer member 1; and 21, a substrate having metal sites 5.
In such a conventional solder supplying method, the holes 2 provided in the transfer member 1 are filled with solder paste 3 as shown in FIG. 22B and then the metal sites 5 (hereinafter referred to as "electrodes") on the substrate 21 and the holes 2 are aligned as shown in FIG. 22C. Then, the solder paste 3 is heated together with the transfer member 1 so as to flow out to thereby form bumps 7 as shown in FIG. 22D.
In the method disclosed in the Examined Japanese Patent Application Publication No. Hei. 7-85487, as shown in FIG. 22A, the holes 2 of the transfer member l do not pass through the transfer member 1 and the holes 2 are formed by drilling. Therefore, if the depths of the holes become different from each other as expressed by holes 2a to 2e in FIG. 23, such a difference directly causes scattering in quantity of solder to be supplied and results in formation of bumps different in height from each other as expressed by bumps 7a to 7e.
Further, because the holes 2 of the transfer member 1 are formed by drilling so as not to pass through the transfer member 1, a longer time is required for drilling to form the holes 2 as the number of bumps 7 increases.
Further, as shown in FIG. 24, because flux (rosin) in a solvent component contained in solder paste is formed as flux residues 8 on the inner walls of the holes 2 after the formation of bumps, a long time is required for cleaning.
Further, a solder material having a high melting point is used in soldered joint portions requiring heat resistance such as soldered joint portions in the inside of an LSI package. When such a high-melting solder material is used for soldering, however, a special member having high heat resistance needs to be used because the quantity of input heat (thermal damage) to peripheral members such as an LSI chip, a printed-wiring substrate, and so on, becomes large.
For example, as disclosed in the Examined Japanese Patent Application Publication No. Hei. 1-266987, there has been proposed a soldering method in which the soldering temperature of a joint portion-requiring high heat resistance is lowered by using in advance solder paste of two kinds of metals having different melting points.
When solder paste of two kinds of metals having different melting points is used in advance, however, coexistence of the two kinds of metals in the paste makes mutual diffusion between the metals progress even at the ordinary temperature in a period of from the point of time when the solder is produced to the point of time when the solder is used. Accordingly, disadvantages such as conglutination of metal particles, or the like, may occur so that the paste cannot be used as solder paste.
In the aforementioned conventional solder supplying method, because the holes 2 to be filled with solder paste 3 are formed by drilling so as not to pass through the transfer member 1, scattering occurs in depth of the holes 2. Accordingly, scattering occurs in height of bumps or a longer time is required for drilling to form the holes 2 as the number of bumps 7 increases. Further, flux (rosin) in a solvent component contained in the solder paste is formed as flux residues 8 on the inner walls of the holes 2 after the formation of bumps.